The present invention relates to an ion exchanger, and more particularly to an ion exchanger which comprises a water-insoluble copolymer obtained by post-polymerizing a fluoroolefin in an aqueous solution of a copolymer of not less than 25% by mole of perfluorovinylacetic acid and vinylidene fluoride.
Ion exchangers are extensively employed in various fields, for instance, desalination of seawater to fresh water, diaphragm process and waste water disposal, and various ion exchangers are developed in compliance with the purposes. In particular, a copolymer of a fluoroolefin and a perfluoroalkylvinyl ether containing sulfonic acid group is known as an ion exchanger having the heat and chemical resistances. However, perfluoroalkylvinyl ethers are very expensive and this ion exchanger has the economic disadvantage. Also, various methods of introducing ion-exchange groups to fluoroolefin polymers for this purpose are known, but have the disadvantage that the products may cause strain, since the fluoroolefin polymers generally have a high crystallinity and the introduction of the ion-exchange groups is liable to occur at the non-crystalline part.
The present inventors have found that a vinylidene fluoride-perfluorovinylacetic acid copolymer containing not less than 25% by mole of the perfluorovinylacetic acid unit has the ion-exchange capacity. However, this polymer is water-soluble and, therefore, cannot be employed as an ion exchanger.